1. Technical Field
The present invention relates to a transport device transporting a medium such as paper and a printing apparatus including the transport device.
2. Related Art
Hitherto, printing apparatuses that print characters or images by discharging ink on a medium which is intermittently transported by a transport unit have been known. Among these printing apparatuses, there is a printing apparatus which includes an imaging unit that images a medium which is transported by a transport unit at each imaging interval, and a control unit that calculates a transport amount of the mediums based on an image which is captured by the imaging unit and controls the transport unit based on the transport amount (for example, JP-A-2011-201152).
Specifically, such a printing apparatus provides feedback on an actual transport amount which is an amount that the medium is actually transported and is calculated based on the image captured by the imaging unit as a controlled transport amount until the transport of the medium is stopped. In this manner, the transport error of the printing apparatus is decreased. The actual transport amount is calculated by integrating the transport amount of the medium at each imaging interval which is calculated based on the image captured at each imaging interval.
However, the printing apparatus described above intermittently transports the mediums. Therefore, a transport period, during which the medium is transported, of the printing apparatus includes a period in which the transport speed is low such as a period immediately after the start of the transport of the medium or a period immediately before the termination of the transport of the mediums, and a period in which the transport is high such as a period during which the medium is transported at a constant speed. In this case, the number of calculations of the transport amount per unit transport amount is likely to be more increased during the period in which the transport speed is low than during the period in which the transport speed is high by the difference between the transport speeds of the medium.
The transport amount at each imaging interval is calculated according to a moved amount of an area including a characteristic pattern in the previous image by specifying which area in the current image the area is moved to. As such, since the transport amount at each imaging interval is calculated based on the image formed of a finite number of pixels, this calculation includes a calculation error due to the quantization in the transport amount at each imaging interval.
Therefore, in a case where the transport amount calculated at each imaging interval is integrated and the actual transport amount during the transport period is calculated, the number of calculations of the transport amount during the period in which the transport speed is low among the transport periods is likely to be increased and the calculation error in accordance with the increase of the number of calculations may affect the calculation accuracy of the actual transport amount.
The above actual circumstances are not limited to the printing apparatus and is substantially common in a transport device which intermittently transports the medium.